1. Field of the Invention
The invention pertains to a protective tube for a piston-cylinder assembly having a piston which is free to move in a cylinder, and a retaining element for the protective tube attached to the piston rod.
2. Description of the Related Art
The protective tube on a piston-cylinder assembly has the job of protecting the piston rod from external influences such as dirt and moisture, and in the case of a shock absorber it also has the task of protecting the assembly from impacts by stones, etc. Because of their location on the vehicle, shock absorbers in particular are subjected to especially severe loads. To achieve long-lasting protection for the piston rod, the protective tube is made of metal and is attached to the piston rod either indirectly by screws or directly by welds. For an example, see FIG. 7.6/47a in Fahrwerktechnik [Chassis Engineering], Jxc3x6rnsen Reimpel, Vol. 3, 1974 edition, p. 42. The metal protective tube is coated to protect it against rust, but it is not always possible to prevent certain areas of the coating from separating from the inside walls of the protective tube during welding. It is very difficult to detect these areas even by a thorough final inspection, and they can be repaired only by a disproportionate amount of work. Precisely in the case of shock absorbers for passenger vehicles, protective tubes of plastic have become widely accepted, since it is known that they cannot rust. In the case of passenger vehicles, the thermal stress on the shock absorbers is usually not as great as in the case of trucks, so that the thermal load limit of a plastic protective tube is not reached when used in this situation. Plastic protective tubes have been known for a long time. As examples, reference can be made to DE 1,951,753 A1, DE 1,951,754 A1, and DE 1,995,281 A1. Plastic tubes, however, suffer in some cases from the disadvantage that it is very difficult to prevent them from assuming a skewed position with respect to the piston rod. In the case of trucks, it must also be anticipated that, on difficult terrain, obstacles will occur which can directly affect the protective tube and cause it is to become skewed.
The task of the present invention is to realize a protective tube for a piston-cylinder assembly which can be manufactured at reasonable cost but which also offers satisfactory protection against corrosion and remains correctly installed for a long time.
In accordance with the invention, the retaining element has a multi-part connecting ring, the parts of which are installed radially toward the piston rod and are in operative connection with it, where the protective tube and the connecting ring parts are connected to each other in such a way that these parts come together to form a connecting ring braced at least in the radial direction.
Regardless of the material of which the protective tube is made, an assembly sequence is possible in which the protective tube is installed after the piston-cylinder assembly has been coated. Precisely in the case of protective tubes made of metal, this possibility offers rather significant advantages, because the protective tube can be a completely finished component.
In another advantageous design, the retaining element has a central support disk, which is connected to the piston rod, the connecting ring acting in the radial direction on the support disk. The support disk can be used as part of an assembly for a bumper. Because the support disk is separate from the protective tube, no forces are introduced into the protective tube when a bumper is used.
For the secure positioning of the protective tube all the way around, the connecting ring has a radial clamping surface and an axial cover surface for the protective tube. The cover surface takes care of the positioning function, but it also serves the function of closing off the end of the protective tube. The end surface of the protective tube therefore does not need to be coated, because the cover surface of the connecting ring also has a sealing effect.
In an advantageous design variant, the clamping and cover surfaces are part of a groove inside the connecting ring, this groove being oriented in the axial direction of the protective tube.
In another design variant, the parts of the connecting ring have means for connecting the ring to the support disk. The need for an assembly device for assembling the connecting ring parts is therefore eliminated, because these parts can be attached individually to the support disk.
For this purpose, the connecting means consist of a profile, which engages with the support disk. The profile can enter into a positive, form-locking connection or into a friction-locking connection with the support disk. For example, the profile can consist of a circumferential groove, into which the support disk fits.
As an alternative, the support disk can have a circumferential rim which extends at least around certain sections of the circumference, to which the connecting ring can be attached. For example, pin-like projections on the connecting ring can engage with the rim of the support disk.
According to one embodiment, the parts of the connecting ring are connected to each other by locking means. This measure greatly simplifies the installation of the protective tube, because it prevents the connecting ring parts from shifting or sliding during the installation of the protective tube.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.